The present invention relates to the production of multiple-layer film or sheeting, and more especially, to an improved process and apparatus for extrusion of multiple-layer sheeting having a layer or layers of polymeric material having desirable surface characteristics. More especially, the present invention comprises the co-extrusion of multiple-layered sheeting, with each layer exhibiting uniform layer thickness across the width thereof, by an apparatus which has an improved laydown means and which is easily adjustable to produce sheeting products having from two to five layers.
Co-extrusion processes for the production of multi-layered sheeting are, of course, well known in the art. However, prior processes do not guarantee, and and often do not produce, co-extruded layers of uniform thickness on the main extruded material. This problem is especially acute when the co-extruded layer comprises a polymeric material having a comparatively low viscosity. Such a material tends to migrate from areas of higher extruder die pressure, to areas of lower extruder die pressure. This results in a sheeting product having varying layer thicknesses across the width of the sheet.
Furthermore, in known processes and apparatus, it was not readily possible to adjust the relative thickness of the various layers, in response to different processing characteristics and/or different requirements for the final products. Furthermore, it was not easy to vary the number of layers to be included in a particular product or to distribute the various layers to give a uniform multiple layer sheet. In these processes, it is often necessary to shut down operation while adjustments and/or modifications are made in the process. A shutdown of this type is extremely time-consuming and expensive due to the cost of labor, materials and lost output.
Thus, the present invention is concerned with an improved laydown means and process for use in the production of multiple-layered sheeting of materials, particularly those which have different processing characteristics, resulting in a uniformity of layer thickness across the entire width of the extruded sheeting.
The present invention is also directed to an improved laydown means for the application of multiple-layers of polymeric material to an initial polymeric base layer, the different polymeric materials in most cases exhibiting different processing characteristics. The laydown device permits easy adjustment of overall layer thickness as well as adjustment of the number of layers.